144 The Irish Naturalist. April, 



tinuous continental range, whose productiveness in the central 

 parts of its area of dispersion is much in excess of what it 

 needs to maintain its numbers; in the less central parts of its 

 range it produces fewer, and, perhaps, still further out, only 

 about the bare number that are necessary, with all allowance 

 for loss, to keep it from decreasing : then at last we come to a 

 zone where it may produce even fewer than the necessary 

 number, a rate of fertility not sufficient to keep up its numbers 

 at all. Even there, it will not die out, but may continue to 

 hold its own, so long as the range of the creature is con- 

 tinuous ; for the innermost parts of the range continue to 

 supply fresh individuals that will fill up the gaps outside 

 But suppose that any part of this outlying range is converted 

 into an island ; then the species is left to its own resources, it 

 can no longer be reinforced as before, and it will become ex- 

 tinct. That may be one of the reasons why in Ireland we 

 want some of the species that maintain themselves in the 

 southern and eastern parts of Great Britain, just as Great 

 Britain also wants some of the species whose continental range 

 extends to within sight of her shores. 



A fortunate chance has preserved to us the Natterjack Toad 

 on the shores of Dingle Bay; but the prima faeie odds against 

 its survival in Ireland must have been large, since we meet 

 it nowhere else in the country. I am disposed to compare 

 with this case of the Natterjack Toad in Kerry the case of that 

 very local little reptile, the Sand Lizard {Laeerta agihs), which 

 we do not find in Ireland, but which is known to occur on 

 the northern shores of the Isle of Man 1 . The Isle of Man 

 has a fauna so very remarkably Irish, that when Professor 

 Carpenter first suggested the use among naturalists of the 

 word " Britannic " for the area comprising both Great Britain 

 and Ireland, and the limitation of the now ambiguous word 



1 See Zoologist, February, 1893 (" Contributions to a Vertebrate Fauna 

 of the Isle of Man," by P. C. Kerrnode) ; also, Mr. P. G. Ralfe's " Birds 

 of the Isle of Man" (1905), where a list of the mammals, reptiles, &c., 

 of the island will be found on page xxxiii. Dr. Scharff has, however, 

 kindly pointed out to me that the records of Laeerta agilis are still in 

 need of confirmation, and the language used by me above is therefore 

 too confident. 



